Intraocular lens

ABSTRACT

An intraocular lens for inhibiting posterior capsular opacification, or secondary cataract, includes an optic having a periphery provided with at least two sharp edges which lie radially spaced from each other with respect to the optical axis of the lens optic.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This is a continuation-in-part application of co-pending U.S.Ser. No. 10/005,864 filed Nov. 8, 2001.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to intraocular lenses (IOLs) forimplantation in an aphakic eye where the natural lens has been removeddue to damage or disease (e.g., a cataractous lens). The presentinvention more particularly relates to a novel IOL designed to inhibitthe unwanted growth of lens epithelial cells (LECs) between the IOL andposterior capsular bag, also known as posterior capsule opacification or“PCO” to those skilled in the art.

[0003] A common and desirable method of treating a cataract eye is toremove the clouded, natural lens and replace it with an artificial IOLin a surgical procedure known as cataract extraction. In theextracapsular extraction method, the natural lens is removed from thecapsular bag while leaving the posterior part of the capsular bag (andpreferably at least part of the anterior part of the capsular bag) inplace within the eye. In this instance, the capsular bag remainsanchored to the eye's ciliary body through the zonular fibers. In analternate procedure known as intracapsular extraction, both the lens andcapsular bag are removed in their entirety by severing the zonularfibers and replaced with an IOL which must be anchored within the eyeabsent the capsular bag. The intracapsular extraction method isconsidered less attractive as compared to the extracapsular extractionmethod since in the extracapsular method, the capsular bag remainsattached to the eye's ciliary body and thus provides a natural centeringand locating means for the IOL within the eye. The capsular bag alsocontinues its function of providing a natural barrier between theaqueous humor at the front of the eye and the vitreous humor at the rearof the eye.

[0004] One known problem with extracapsular cataract extraction isposterior capsule opacification, or secondary cataract, whereproliferation and migration of lens epithelial cells occur along theposterior capsule behind the IOL posterior surface which creates anopacification of the capsule along the optical axis. This requiressubsequent surgery, such as an Er:YAG laser capsulotomy, to open theposterior capsule and thereby clear the optical axis. Undesirablecomplications may follow the capsulotomy. For example, since theposterior capsule provides a natural barrier between the back of the eyevitreous humor and front of the eye aqueous humor, removal of theposterior capsule allows the vitreous humor to migrate into the aqueoushumor which can result in serious, sight-threatening complications. Itis therefore highly desirable to prevent posterior capsule opacificationin the first place and thereby obviate the need for a subsequentposterior capsulotomy.

[0005] Various methods have been proposed in the art to prevent or atleast minimize PCO and thus also the number of Er:YAG laser capsultomiesrequired as a result of PCO. These PCO prevention methods include twomain categories: mechanical means and pharmaceutical means.

[0006] In the mechanical means category of PCO prevention, efforts havebeen directed at creating a sharp, discontinuous bend in the posteriorcapsule wall which is widely recognized by those skilled in the art asan effective method for minimizing PCO. See, for example, PosteriorCapsule Opacification by Nishi, Journal of Cataract & RefractiveSurgery, Vol. 25, January 1999. This discontinuous bend in the posteriorcapsule wall can be created using an IOL having a posterior edge whichforms a sharp edge with the peripheral wall of the IOL.

[0007] In the pharmaceutical means of PCO prevention, it has beenproposed to eliminate LEC and/or inhibit LEC mitosis by using anLEC-targeted pharmaceutical agent. See, for example, U.S. Pat. No.5,620,013 to Bretton entitled “Method For Destroying Residual LensEpithelial Cells”. 195

[0008] While this approach is logical in theory, putting such a methodinto clinical practice is difficult due to complications arising, forexample, from the toxicity of some of the LEC inhibiting agentsthemselves (e.g., saporin), as well as the difficulty in ensuring atotal kill of all LECs in the capsular bag. Any remaining LECs mayeventually multiply and migrate over the IOL, eventually resulting inPCO despite the attempt at LEC removal at the time of surgery.

[0009] By far the most promising method for inhibiting LEC formation onthe posterior surface of an IOL is the mechanical means, i.e., bydesigning the IOL to have a sharp peripheral edge particularly at theposterior surface—peripheral edge juncture to create a discontinuousbend in the posterior capsule wall. This discontinuous bend in theposterior capsule wall has been clinically proven to inhibit the growthand migration of LECs past this bend and along the IOL surface. One ofthe early reports of this PCO-inhibiting effect of a planoconvex IOL maybe found in Explanation of Endocapsule Posterior Chamber Lens AfterSpontaneous Posterior Dislocation by Nishi et al, J Cataract &Refractive Surgery-Vol 22, March 1996 at page 273 wherein the authorsexamined an explanated planoconvex PMMA IOL where the posterior surfaceof the IOL was planar and formed a square edge with the peripheral edgeof the IOL:

[0010] “Macroscopic view of the explanted IOL and capsule revealed a 9.5mm capsule diameter. The open circular loops fit well along the capsuleequator. The capsule equator not in contact with the haptic was alsowell maintained (FIG. 3). An opaque lens mass (Soemmering's ringcataract) was seen between the haptics and optic. The posterior capsulefacing the IOL optic was clear.

[0011] Histopathological examination of the explanted capsule revealedfew epithelial cells (LECs) on the posterior capsule. Between the loopsand the optic, a lens mass with accumulation at the edge of the opticwas seen (FIG. 4). There was an obvious bend in the posterior capsule atthis site.” (Emphasis added.)

[0012] Thus, in the years since this report, the industry has seen muchactivity on creating IOLs with sharp posterior edges so as to create asharp, discontinuous bend in the posterior capsule wall. While IOLshaving a sharp posterior edge have proven to inhibit PCO compared toIOLs having rounded edges at the posterior surface-peripheral edgejuncture, there still remains the possibility of LECs migrating alongthe posterior capsule and behind the IOL surface, especially if there isuneven contact and force of the IOL periphery with the capsular bag.This may happen, for example, should the IOL move within the capsularbag following surgery. There therefore remains a need for an improvedIOL design which addresses the problem of LEC migration and subsequentPCO formation despite having an IOL with a single sharp posterior edge.

SUMMARY OF THE INVENTION

[0013] The present invention addresses the problem of PCO formationbeyond the first sharp posterior edge of an IOL by providing an IOLhaving a periphery including at least two, radially spaced, sharp edgesdefined by the posterior edge and peripheral walls which extendsubstantially parallel to the optical axis of the IOL and an intercedingperipheral wall which extends substantially perpendicular to the opticalaxis. This configuration of the periphery of the IOL optic is asignificant improvement over the single square edge optic designs inthat it provides improved barriers against LEC migration. In analternate embodiment, the inner-most edge which is defined in part bythe posterior surface is sharp while the second, outer edge is roundedabout at least a portion of the circumference thereof. The opticperiphery design is also relatively easy to manufacture compared withother, more complicated IOL periphery designs which have been proposedin the prior art for inhibiting LEC migration. See, for example, thefollowing patents and publications which show various IOL opticperiphery designs:

[0014] U.S. Pat. No. 5,171,320 issued to Nishi on Dec. 15, 1992

[0015] U.S. Pat. No. 5,693,093 issued to Woffinden et al on Dec. 2, 1997

[0016] U.S. Pat. No. 6,162,249 issued to Deacon et al on Dec. 19, 2000

BRIEF DESCRIPTION OF THE DRAWING

[0017]FIG. 1 is a cross-sectional view of a human eye showing thenatural lens within the capsular bag of the eye;

[0018]FIG. 2 is a cross-sectional view of a human eye showing thenatural lens removed and replaced with a prior art IOL;

[0019]FIG. 3 is a plan view of a prior art IOL;

[0020]FIG. 4a is a plan view of an IOL made in accordance with thepresent invention;

[0021]FIG. 4b is a cross-sectional view of the inventive IOL as takengenerally along the line 4 b-4 b of FIG. 4a;

[0022]FIG. 5 is an enlarged, fragmented, cross-sectional view showingthe detail of the peripheral wall configuration of the IOL of thepresent invention;

[0023]FIG. 6 is the view of FIG. 5 showing an alternate embodiment ofthe peripheral wall configuration of the IOL of the present invention;and

[0024]FIG. 7 is the view of FIG. 5 showing an alternate embodiment ofthe invention.

DETAILED DESCRIPTION

[0025] Referring now to the drawing, there is seen in FIG. 1 across-sectional view of a human eye 10 having an anterior chamber 12 anda posterior chamber 14 separated by the iris 30. Within the posteriorchamber 14 is a capsule 16 which holds the eye's natural crystallinelens 17. Light enters the eye by passing through the cornea 18 to thecrystalline lens 17 which act together to direct and focus the lightupon the retina 20 located at the back of the eye. The retina connectsto the optic nerve 22 which transmits the image received by the retinato the brain for interpretation of the image.

[0026] In an eye where the natural crystalline lens has been damaged(e.g., clouded by cataracts), the natural lens is no longer able toproperly focus and direct incoming light to the retina and images becomeblurred. A well known surgical technique to remedy this situationinvolves removal of the damaged crystalline lens which may be replacedwith an artificial lens known as an intraocular lens or IOL such asprior art IOL 24 seen in FIGS. 2 and 3. Although there are manydifferent IOL designs as well as many different options as to exactplacement of an IOL within an eye, the present invention concerns itselfwith an IOL for implanting inside the substantially ovoid-shaped capsule16 of eye 10. This implantation technique is commonly referred to in theart as the “in-the-bag” technique. In this surgical technique, a part ofthe anterior portion of the capsular bag is cut away (termed a“capsularhexis”) while leaving the posterior capsule 16 a intact andstill secured to the ciliary body 26.

[0027] Thus, in the “in-the-bag” technique of IOL surgery, the IOL isplaced inside the capsule 16 which is located behind the iris 30 in theposterior chamber 14 of the eye. An IOL includes a central optic portion24 a which simulates the extracted natural lens by directing andfocusing light upon the retina, and further includes a means forsecuring the optic in proper position within the capsular bag. A commonIOL structure for securing the optic is called a haptic which is aresilient structure extending radially outwardly from the periphery ofthe optic. In a particularly common IOL design, two haptics 24 b, 24 cextend from opposite sides of the optic and curve to provide a biasingforce against the inside of the capsule which secures the optic in theproper position within the capsule (see FIG. 2).

[0028] As stated in the Background section hereof, an undesirablepost-surgical condition known as posterior capsule opacification or PCOmay occur which results in an implanted IOL becoming clouded and thus nolonger able to properly direct and focus light therethrough. The maincause for this condition is the mitosis and migration of lens epithelialcells (LECs) across the posterior surface of the capsule behind the IOLoptic. As seen in FIG. 2, the posterior surface 16 a of the capsule 16touches the posterior surface of the IOL optic 24 a. When the damagednatural lens is surgically removed, a number of LECs may remain withinthe capsule 16, particularly at the equator 16 b thereof which is theprinciple source of germinal LECs. Although a surgeon may attempt toremove all LECs from the capsular bag at the time of IOL implantationsurgery, it is nearly impossible to remove every single LEC. Anyremaining LECs can multiply and migrate along the posterior capsule wall16 a. This is especially true in IOLs having rounded edges, where it hasbeen found that clinically significant PCO results in about 20%-50% ofpatients three years post surgery. A presently popular and effectivemethod of preventing PCO is to create a sharp, discontinuous bend in theposterior capsule wall 16 a as explained in the Background sectionhereof.

[0029] Referring now to FIGS. 4a,b and 5, a first embodiment of theinventive IOL 32 is shown. IOL 32 is seen to include a central opticportion 34 having opposite anterior and posterior surfaces 34 a and 34b, respectively. When implanted within the eye, anterior optic surface34 a faces the cornea 18 and posterior optic surface 34 b faces theretina 20. A pair of haptics 36,38 are attached to and extend fromopposite sides of the periphery of optic portion 34 and are configuredto provide a biasing force against the interior of the capsule 16 toproperly position IOL 32 therein. More particularly, the haptics 36,38are configured such that upon implanting the IOL with the capsular bag,the haptics engage the interior surface of the capsular bag. Theengagement between the haptics and capsule creates a biasing forcecausing the IOL optic 34 to vault posteriorly toward the retina 20whereupon the posterior surface 34 b of the IOL optic presses tightlyagainst the interior of the posterior capsule wall 16 a of capsule 16.It is noted that other known IOL positioning means are possible andwithin the scope of the invention. Furthermore, IOL 32 may be made fromany suitable IOL material, e.g., PMMA, silicone, hydrogels andcomposites thereof. The IOL 32 may also be a one piece or multiple piecedesign (e.g. where the haptics are attached to the optic after the opticis formed.)

[0030] Referring still to FIGS. 4a,b and 5, it is seen that IOL optic 34has a periphery including a first sharp edge E1 defined at the junctureof posterior surface 34 b and peripheral wall P₁. With the haptics 36,38providing the biasing force explained above, the optic posterior surface34 b presses tightly against the posterior capsule wall 16 a. Sincecapsule 16 is somewhat resilient in nature, the force of the IOL opticagainst the capsule wall results in the IOL indenting into the posteriorcapsule wall. The first sharp edge E₁ of the IOL optic thus forciblyindents into the capsule wall and thereby creates a discontinuous bendin the posterior capsule wall at this point as indicated at arrow B1 inFIGS. 5 and 6. As explained above, this discontinuous bend B1 in theposterior capsule wall 16 a acts to inhibit LEC migration past thispoint (i.e., between the posterior capsule wall 16 a and IOL posteriorsurface 34 b) and PCO is inhibited.

[0031] Referring still to FIG. 5, it is seen that the periphery of IOLoptic 34 further includes an inner right angle corner C₁ defined at thejuncture of first peripheral wall P₁ and second peripheral wall P₂ whichare oriented substantially perpendicular to each other. A second sharpedge E₂ is defined at the juncture of peripheral walls P₂ and P₃ whichalso lie substantially perpendicular to each other. The provision of atleast two sharp edges E₁ and E₂ in the periphery of the IOL opticprovides multiple barriers against migrating LECs.

[0032] It is noted that the degree to which the IOL indents into theposterior capsule may vary among patients. In some patients, the IOL mayindent such that only first sharp edge E₁ is engaging the posteriorcapsule in which case a single discontinuous bend B₁ would be providedin the capsule wall to inhibit LEC migration. In this situation, secondsharp edge E₂ still provides a discontinuous geometry which acts todiscourage LECs which may have attached to the IOL from migrating towardand onto the anterior surface 34 a of the IOL optic. In other patients,the IOL may indent further into the posterior capsule in which case bothfirst sharp edge E₁ and second sharp edge E₂ are engaging the posteriorcapsule (FIG. 5), thereby creating first and second bends B₁ 241 and B₂therein, respectively. Thus, in either case, LEC migration is inhibited.

[0033] As mentioned above, the primary source of germinating LECs is atthe equator 16 b of the capsular bag which is located radially outwardlyof the optic periphery (FIG. 2). As LECs multiply, they begin migratingradially inwardly along the capsular bag. In a patient where the opticindents into the posterior capsule as seen in FIG. 5, once the LECsreach the IOL optic 34, they will encounter second sharp bend B₂ in thecapsule formed by IOL sharp edge E₂. This sharp bend B₂ provides thefirst barrier against migrating LECs. However, should any LECs continueto migrate inwardly past the bend B, they will then encounter firstsharp bend B in the capsule. The provision of more than one sharp bendin the capsule provides more than one barrier against migrating LECs.The present invention thus provides a peripheral edge configurationsubstantially preventing the chance of LEC migration along the posteriorcapsule.

[0034] It is furthermore noted that the multiple sharp edgeconfiguration of the inventive IOL provides a more complex frillformation in the capsule than the single sharp edge IOL designs of theprior art. In this regard, see the Nishi article cited herein (JCRSJanuary 1995) which explains how it is the complex frill formation atthe capsular bend which is believed to inhibit LEC migration.

[0035] A presently preferred method of forming the multiple sharp edgeconfiguration in the IOL optic 34 comprises a milling operation wherethe IOL optic is mounted to a fixture and a mill is used to cut into theposterior optic surface at the perimeter thereof. The depth of the millcut, as measured from the edge of posterior surface 34 b to surface wallP₂, is preferably about 0.01-1.5 mm, more preferably about 0.05-1.0 mm,and most preferably is about 0.08 mm. The width of the mill cut, asmeasured from wall P1 to wall P₃, is preferably at least about 0.03 mm.Other methods which may be employed to form the peripheral edge geometryinclude lathing and molding, for example. It is also preferred that IOL32 undergo tumble polishing prior to forming the edge geometry so as toensure the edges E₁, E₂, E₃, etc., retain their sharpness.

[0036]FIG. 6 shows an alternate embodiment of the inventive IOL whichfurther includes a third sharp edge E₃ which is defined at the junctureof perpendicular wall surfaces P₄ and P₅. FIG. 6 illustrates third sharpedge E₃ as not engaging capsule 16, however, it is possible that in somepatients the optic periphery will indent even deeper into the capsulewall whereupon sharp edge E₃ would engage the capsule wall. If the thirdsharp edge E₃ does in fact engage the capsule wall, a third bend in thecapsule wall (not shown) would form, providing yet another barrieragainst LEC migration as explained with respect to sharp edges E₁ and E₂above. In the case where third sharp edge E₃ does not engage thecapsule, it still provides a discontinuous geometry which acts todiscourage LECs which may have attached to the IOL from migrating towardand onto the anterior surface 34 a of the IOL optic. It will thus beappreciated that the unique multiple sharp edge geometry of the presentinvention provides multiple barriers against LEC migration bothposteriorly and anteriorly of the optic regardless of how deeply theoptic indents into the posterior capsule.

[0037] It is thus seen that the sharp edges are formed in a radiallyspaced configuration which gives a “stepped” configuration to the IOLoptic periphery. It will be appreciated that any number of sharp edgesmay be provided in the stepped edge configuration described herein.Moreover, the peripheral wall surfaces P₁, P₃, P₅ extend along spaced,parallel planes which extend substantially parallel to the optical axisOA of the IOL optic (see FIGS. 4a,b), while the interceding peripheralwall surfaces P₂ and P₄ extend along planes which are substantiallyperpendicular to the optical axis OA. This unique peripheralconfiguration provides an IOL which substantially inhibits PCO asdescribed above.

[0038]FIG. 7 shows yet a further embodiment of the invention where thesecond edge is not sharp, but rather includes a rounded edge E_(R). Asstated previously, the first sharp edge E₁ may alone be sufficient toprevent LECs from migrating past to the posterior surface. Thus, in thisembodiment, the second edge E_(R) may have a curved radius about atleast a portion of the circumference thereof which may be useful forother reasons (e.g., preventing glare). The haptics may advantageouslybe attached to second edge ER and/or peripheral wall P₃.

What is claimed is:
 1. An intraocular lens for implanting in a humaneye, comprising: a) a lens optic having opposite anterior and posteriorsurfaces defined by an optic periphery and an optical axis extendingfrom said anterior surface to said posterior surface; and b) at leasttwo edges formed in said optic periphery wherein, with respect to saidoptical axis, said second edge is located radially outwardly of saidfirst edge, said first edge being sharp and defined by said opticposterior surface and a first peripheral wall extending about the entireoptic periphery and lying substantially parallel to said optical axis.2. The intraocular lens of claim 1, and further comprising locatingmeans attached adjacent said second edge, said locating means operableto position and maintain said intraocular lens in said human eye in thecorrect location.
 3. The intraocular lens of claim 2, wherein saidlocating means comprises one or more haptics.
 4. The intraocular lens ofclaim 1, wherein at least a portion of said second edge has a curvedradius.